Arnold B A, Scheibe P O
AJR Am J Roentgenol. 1984 Mar;142(3):609-13. doi: 10.2214/ajr.142.3.609.
The sources of noise in a digital video subtraction angiography system were identified and analyzed. Signal-to-noise ratios of digital radiography systems were measured using the digital image data recorded in the computer. The major sources of noise include quantum noise, TV camera electronic noise, quantization noise from the analog-to-digital converter, time jitter, structure noise in the image intensifier, and video recorder electronic noise. A new noise source was identified, which results from the interplay of fixed pattern noise and the lack of image registration. This type of noise may result from image-intensifier structure noise in combination with TV camera time jitter or recorder time jitter. A similar noise source is generated from the interplay of patient absorption inhomogeneities and patient motion or image re-registration. Signal-to-noise ratios were measured for a variety of experimental conditions using subtracted digital images. The measured signal-to-noise ratios were found to fluctuate on repeat trials with about a 10% standard deviation. Averaging of video frames was found to reduce the noise level by the expected square root N relation, where N is the number of frames averaged. Image-intensifier structure noise was shown to be a dominant noise source in unsubtracted images at medium to high radiation exposure levels. A total-system signal-to-noise ratio (SNR) of 750:1 was measured for an input exposure of 1 mR/frame at the image intensifier input. The effect of scattered radiation on subtracted image SNR was found to be greater than previously reported. The detail SNR was found to vary approximately as one plus the scatter degradation factor. Quantization error noise with 8-bit image processors (signal-to-noise ratio of 890:1) was shown to be of increased importance after recent improvements in TV cameras. The results of the analysis are useful both in the design of future digital radiography systems and the selection of optimum clinical techniques.
对数字视频减影血管造影系统中的噪声源进行了识别和分析。利用计算机中记录的数字图像数据测量了数字射线摄影系统的信噪比。主要噪声源包括量子噪声、电视摄像机电子噪声、模数转换器的量化噪声、时间抖动、图像增强器中的结构噪声以及视频记录器电子噪声。识别出一种新的噪声源，它是由固定模式噪声和图像配准不足的相互作用导致的。这种类型的噪声可能是由图像增强器结构噪声与电视摄像机时间抖动或记录器时间抖动共同作用产生的。类似的噪声源是由患者吸收不均匀性与患者运动或图像重新配准的相互作用产生的。使用减影数字图像在各种实验条件下测量了信噪比。发现重复试验时测量的信噪比波动，标准偏差约为10%。发现对视频帧进行平均可按预期的平方根N关系降低噪声水平，其中N是平均的帧数。在中高辐射暴露水平下，图像增强器结构噪声被证明是未减影图像中的主要噪声源。在图像增强器输入端输入1 mR/帧时，测量的全系统信噪比（SNR）为750:1。发现散射辐射对减影图像SNR的影响比先前报道的更大。发现细节SNR大致随1加上散射退化因子而变化。在电视摄像机最近改进后，8位图像处理器的量化误差噪声（信噪比为890:1）显示出越来越重要。分析结果对未来数字射线摄影系统的设计和最佳临床技术的选择都很有用。
